The long term objective of this proposal is to detect and microbiologically characterize the initial periodontal lesion. Current information on the rate of disease activity in such subjects is minimal. This investigation compares the clinical and microbiological characteristics of the initial lesion of adult periodontitis, with gingivitis and health. Clinical, microbial and immunologic features will be sought that discriminate between progressive attachment loss, gingivitis, and health. The first aim will determine clinical features of the initial periodontal lesion in adults. Healthy and gingivitis subjects will be monitored longitudinally using electronic temperature and attachment level probes seeking sites showing significant losses in periodontal attachment level (disease activity). The gingivitis population will be enriched for active sites by screening for subjects with elevated subgingival temperatures. Comparison of clinical characteristics of sites and subjects with active lesions, with gingivitis sites from gingivitis subjects, and healthy sites from healthy subjects, should indicate which features are related to disease activity, and whether any clinical features including increased temperature are indicators for elevated risk for disease activity. To determine the etiology of the initial periodontal lesion, the predominant cultivable microbiota will be determined from disease active sites, and compared with that of gingivitis sites in gingivitis subjects, and with healthy sites in healthy subjects. Comparison of the microbiota of active lesions with gingivitis and healthy sites should indicate which species are related to progressive disease, and whether any microorganisms are useful indicators of the risk for conversion of health or gingivitis to active disease. Serum antibodies will be sought to dominant subgingival species to immunologically characterize the initial periodontal lesion. Ultimately, this information will contribute to early identification of subjects at elevated risk for onset of periodontitis, and improve our understanding of the initial stage of periodontal disease.